1. Technical Field
The present invention relates to wireless communication systems, wireless communication apparatuses, wireless communication methods, and computer programs which mutually perform communication between a plurality of wireless stations in a wireless LAN (Local Area Network) or the like. In particular, the present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program which efficiently transmit isochronous data, such as AV content.
More specifically, the present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program which efficiently transmit isochronous data in an ad-hoc (ad-hoc) communication environment in which individual communication stations forms a network in an autonomous distributed manner without the relationship of a controlling station and a controlled station. In particular, the present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program which perform data transmission with a guaranteed bandwidth in an ad-hoc communication environment.
2. Background Art
As a system for freeing users from LAN wiring of a wired scheme, wireless LANs are gaining attention. Since wireless LANs can omit a majority of wire cables in work spaces such as offices, communication terminals, such as personal computers (PCs), can be moved with relative ease.
In recent years, in conjunction with an increased speed and reduced cost of wireless LAN systems, the demand thereon has increased considerably. In particular, recently, in order to construct a small-scale wireless network with multiple pieces of electronic equipment available around people to perform information communication, the incorporation of a personal area network (PAN) is under consideration. For example, frequency bands, such as a 2.5 GHz band, a 5 GHz band, and so on, that do require a license of a regulatory agency, are utilized to define different wireless communication systems.
A method that is typically used to configure a local area network using a wireless technology is that one apparatus that serves as a controlling station, called an “access point”, is provided in an area to form a network under the centralized control of the controlling station. In this case, the access point provides synchronization between communication apparatuses in the wireless network. Access control based on band reservation is performed. That is, a communication apparatus that attempts to perform isochronous communication first makes a reservation with the access point for a band required for the information transmission and utilizes a transmission path so that the information transmission does not collide with information transmission of another communication apparatus.
However, when asynchronous communication is performed between a transmitting-side communication apparatus and a receiving-side communication apparatus, wireless communication that goes through an access point is always required. Thus, there is a problem in that the utilization efficiency of a transmission path is reduced by half.
In contrast, “ad-hoc (ad-hoc) communication”, in which terminals perform wireless communication with each other directly, has been proposed. In particular, in a small-scale wireless network constituted by a relatively small number of clients located in the vicinity, ad-hoc communication that allows arbitrarily terminals to perform wireless communication with each other without use of a particular access point is considered to be appropriate.
For example, a mode that operates on a peer-to-peer (peer to peer) basis in an autonomous distributed manner without the provision of a controlling station has been prepared for a wireless LAN system based on IEEE 802.11.
On the other hand, in order to transfer isochronous and time-sequence data, such as AV content for which data needs to be transmitted periodically at regular intervals, a bandwidth must be guaranteed.
For example, IEEE 802.11 TG-e is promoting a study for a communication method based on the premise of bandwidth guarantee using a wireless LAN system.
However, when an attempt is made to guarantee a bandwidth in a conventional wireless LAN system, a typically used approach is that a specific controlling station is defined so as to centrally control communication resources and to specify time that is activated in a limited manner in a certain group. The right of transmission is centrally generated at a communication apparatus that serves as a transmitting end of information and a wireless communication apparatus that serves as a receiving end is dependent on and is controlled by the transmitting-end communication apparatus.
This case is based on a premise that a communication apparatus that serves as the specific controlling station is defined, and is not applicable to a system in which the controlling-station apparatus is not provided. In particular, when bandwidth-reservation-based communication is implemented by forming an ad-hoc network without the relationship of a controlling station and a controlled station, it is difficult to determine to which range of influence should be considered. Further, since the right of transmission is centrally generated at a communication apparatus that serves as a transmitting end of information, a notification cannot be issued to indicate that a wireless communication apparatus that serves as a receiving end is in use for receiving a signal at a predetermined timing.
Also, isochronous communication is performed to transmit isochronous data, i.e., time-sequential data. In this case, a predetermined communication band (or time) for isochronous communication is reserved in advance and specific communication apparatuses exclusively perform communication with each other in the communication band (or time).
For example, as a technology that is currently being standardized for a wireless personal area network (WPAN) based on IEEE 802.15.3, a scheme is considered in which a predetermined communication band is reserved as a guaranteed time slot (GTS) so that isochronous communication is performed in the band.
However, in the conventional wireless LAN system, when an attempt is made to perform bandwidth-guaranteed communication such as isochronous communication, there is a need for a scheme for sharing the amount of its guaranteed bandwidth with another communication apparatus. Thus, a communication apparatus that serves as a particular controlling station needs to be defined so as to centrally manage the amount of communication. In other words, such communication with a guaranteed bandwidth is not directly applicable to a wireless communication system that does not have the relationship of a controlling station and a controlled station.
Further, communication between other apparatuses needs to be prevented from communicating with each other at time when isochronous communication is performed. Thus, in this respect, the controlling station also needs to centrally identify the communication apparatuses that use the time. That is, it is extremely difficult to realize band-reservation-based communication, such as isochronous communication, by forming an ad-hoc network.